Hybridized wideband notch filter topologies and methods

ABSTRACT

Radio frequency (RF) acoustic wave resonator (AWR) filter circuits and methods. Embodiments essentially de-couple the stopband or notch characteristics of an RF filter from the passband characteristics. Accordingly, the de-coupled parameters can be individually designed to meet the specifications of a particular application. Partially-hybridized or fully-hybridized series-arm and parallel-arm AWR filter building blocks enable “de-coupled” RF filters having (1) wideband and low insertion loss passbands and (2) wideband deep notches (stopbands) with a specifically placed notch center frequency, without compromising the passband characteristics. The AWR filter building blocks include an inductance L that matches (resonates with) the electrostatic capacitance CO of the corresponding AWR within a desired passband. The resonance and anti-resonance frequencies of the building block AWRs are selected to be spaced apart from the specified passband in order to provide independent stopband or notch characteristics without substantially affecting the passband characteristics.

BACKGROUND (1) Technical Field

This invention relates to electronic circuits, and more particularly toradio frequency electronic circuits and related methods.

(2) Background

Many modern electronic systems include radio frequency (RF)transceivers; examples include cellular telephones, personal computers,tablet computers, wireless network components, televisions, cable system“set top” boxes, automobile communication systems, wireless sensingdevices, and radar systems. Many RF transceivers are quite complextwo-way capable of transmitting and receiving in duplex or half-duplexmodes across multiple frequencies in multiple bands; for instance, inthe United States, the 2.4 GHz band is divided into 14 channels spacedabout 5 MHz apart. As another example, a modern “smart telephone” mayinclude RF transceiver circuitry capable of concurrently operating ondifferent cellular communications systems (e.g., GSM, CDMA, LTE, and 5Gin multiple bands within the 600-6000 MHz range), on different wirelessnetwork frequencies and protocols (e.g., various IEEE 802.11 “WiFi”protocols at 2.4 GHz and 5 GHz), and on “personal” area networks (e.g.,Bluetooth based systems).

A simple radio system generally operates in one radio frequency (RF)band for transmitting RF signals and a separate RF band for receiving RFsignals. An RF band typically spans a range of frequencies (e.g., 10 to100 MHz per band), and actual signal transmission and reception may bein sub-bands or channels of such bands, which may overlap.Alternatively, two widely spaced RF bands may be used for signaltransmission and reception, respectively.

More advanced radio systems, such as some cellular telephone systems,may be operable over multiple RF bands for signal transmission andreception, but at any one time still use only one transmit sub-band andone receive sub-band within a single RF band, or only two widely spacedtransmit and receive RF bands. Such multi-band operation allows a singleradio system to be interoperable with different international frequencyallocations and signal coding systems (e.g., CDMA, GSM). For someapplications, international standards bodies have labeled commonfrequency bands with labels. For instance, bands covered by the LTEstandard are commonly labeled a “Bn” (e.g., B1, B3, B7); one listing ofsuch bands may be found athttps://en.wikipedia.org/wiki/UMTS_frequency_bands. As another example,bands covered by the fifth generation (5G) technology standard forbroadband cellular networks are commonly labeled from n1 to n98; see,for instance, the listing athttps://en.wikipedia.org/wiki/5G_NRfrequency_bands.

In recent years, a technique called “Carrier Aggregation” (CA) has beendeveloped to increase bandwidth for RF radio systems, and inparticularly cellular telephone systems. In one version of CA known as“inter-band” mode, cellular reception or transmission may occur overmultiple RF bands simultaneously (e.g., RF bands B1, B3, and B7). Thismode requires passing the receive or transmit RF signal through multipleband filters simultaneously, depending on the required band combination.

A design challenge in advanced radio systems is dealing with RFinterference. For instance, simultaneous asynchronous transmission andreception over different nearby bands generally causes RF noise/leakagefrom transmission over one band to interfere with reception over anotherband. As one example, cellphone transmission at the low end of the n41band (2496-2690 MHz) may generate noise/leakage in the n40 band(2300-2400 MHz) between cellphones as well as within the transmittingcellphone. In addition, cellphone transmission over the n41 band maygenerate noise/leakage in the 2.4 GHz WiFi band (2402-2480 MHz).

RF interference may also arise in systems using inter-band carrieraggregation with non-contiguous resource block allocation (e.g., bandsn77 and n79). Transmission leakage may impact reception within the samecommunication device despite antenna and diplexer isolation. As anotherexample, communication devices (e.g., cellphones) that operate overdifferent generations of band allocations (e.g., LTE and NR bands suchas B42 and n79) may similarly experience interference on the receptionpath from self-transmissions.

Conventionally, notch and bandpass filters have been used to isolate orpass RF signals within a transceiver. For example, FIG. 1 is asimplified block diagram of a prior art transceiver 100. Radiofrequencies received by an antenna 102 may be directed by means of arouting device (e.g., a switch or a diplexer) 104 to a receive path. Thereceive path generally includes a set of RF filters 106 that provide afiltered RF output to one or more low-noise amplifiers (LNAs) 108, whichprovide an amplified RF signal to reception (Rx) mixing, backend, andbaseband circuitry 110. Transmission (TX) mixing, backend, and basebandcircuitry 112 provides an outgoing RF signal to one or more poweramplifiers (PAs) 114. The amplified output of PAs 114 is processedthrough a set of RF filters 116 before being conveyed to the routingdevice 104 and transmitted by the antenna 102.

The Tx and Rx filters 106, 116 often comprise sets of one or more notchfilters and/or bandpass filters per band or aggregation of bands. Aparticular challenge is designing filters that provide a high level ofattenuation (e.g., for some bands, at least 25 dB, and preferably morethan 30 dB) for the notch filters to eliminate unwanted Tx noise/leakagewithout necessarily decreasing Tx power and/or restricting resourceallocation in the Tx band. It is also desirable to have flexible notchfiltering solutions that can be optimized and/or reconfigured fordifferent bands and combinations or aggregations of bands, or fordifferent telecommunication system operators in different regions.

SUMMARY

The invention encompasses high performance radio frequency (RF) acousticwave resonator (AWR) filter circuits and methods for designing suchfilter circuits. The inventive RF filter circuits provide a high levelof attenuation at selected frequencies to eliminate unwanted RFtransmission (Tx) noise/leakage without necessarily decreasing Tx powerand/or restricting resource allocation in the Tx band. Embodimentsinclude flexible notch filtering solutions that can be optimized and/orreconfigured for different bands and combinations or aggregations ofbands, or for different telecommunication system operators in differentregions.

Embodiments essentially de-couple the stopband or notch characteristicsof an RF filter from the passband characteristics of the RF filter.Accordingly, each of those de-coupled parameters can be individuallydesigned to meet the specifications of a particular application.Partially-hybridized or fully-hybridized series-arm and parallel-arm AWRfilter building blocks in accordance with the present invention can beused to build RF filters having “de-coupled” or essentially independentpassband and stopband characteristics. Such “de-coupled” RF filters canhave (1) wideband and low insertion loss passbands and (2) wideband deepnotches (stopbands) with a specifically placed notch center frequency,without compromising the passband characteristics.

Embodiments include series-arm and parallel-arm AWR filter buildingblocks each having an inductance L that matches (resonates with) theelectrostatic capacitance C0 of the corresponding AWR within a desiredpassband. The series-arm and parallel-arm AWR filter building blocks aredesigned such that both the resonance frequency and the anti-resonancefrequency of the respective AWR are selected to be spaced apart infrequency from the specified passband for the corresponding buildingblock, in order to provide independent stopband or notch characteristicswithout substantially affecting the passband characteristics.

Methods encompassed by the present invention include selecting aseries-arm AWR having an electrostatic capacitance C0 small enough to becompatible with a deep stopband/notch, whose resonance frequency andanti-resonance frequency are spaced apart in frequency from a desiredpassband; selecting a parallel-arm AWR having an electrostaticcapacitance C0 large enough to be compatible with a deep stopband/notchand larger than the electrostatic capacitance C0 of the series-arm AWR,whose resonance frequency and anti-resonance frequency are spaced apartin frequency from the desired passband; coupling the parallel-arm AWR ina shunt configuration with the series-arm AWR; tuning out theelectrostatic capacitance C0 of the series-arm AWR within the desiredpassband; and tuning out the electrostatic capacitance C0 of theparallel-arm AWR within the desired passband, wherein the series-arm AWRand the parallel-arm AWR resonance frequencies and the anti-resonancefrequencies define a notch band for the radio frequency filter circuit.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a prior art transceiver.

FIG. 2 is a diagram of a common symbol for an acoustic wave resonator(AWR) and the equivalent circuit model for an AWR.

FIG. 3 is a graph of the impedance of two prior art ideal AWRs as afunction of frequency.

FIG. 4 is a schematic diagram of a simple series-arm AWR filter buildingblock in accordance with the present invention.

FIG. 5 is a schematic diagram of an advanced series-arm AWR filterbuilding block in accordance with the present invention.

FIG. 6 is a schematic diagram of a simple parallel-arm AWR filterbuilding block in accordance with the present invention.

FIG. 7 is a schematic diagram of an advanced parallel-arm AWR filterbuilding block in accordance with the present invention.

FIG. 8 is a schematic diagram of a L-type RF filter that combines oneseries-arm AWR filter building block with one parallel-arm AWR filterbuilding block.

FIG. 9 is a schematic diagram of a Pi-type RF filter that combines oneseries-arm AWR filter building block with two bracketing parallel-armAWR filter building blocks.

FIG. 10 is a schematic diagram of a T-type RF filter that combines twoseries-arm AWR filter building blocks with one intermediate parallel-armAWR filter building block.

FIG. 11 is a block diagram a four-resonator “laddered” RF filter thatcombines two series-arm AWR filter building blocks, (in this example,with Notch Tuning and AWR Match Adjustment circuitry) and twoparallel-arm AWR filter building blocks, (in this example, with NotchTuning and AWR Match Adjustment circuitry).

FIG. 12A is a process flow chart showing a summarized methodology fordesigning RF filters having essentially independent passband andstopband characteristic, and encompasses both partially-hybridized andfully-hybridized filter networks.

FIG. 12B is a process flow chart showing a detailed methodology fordesigning a particular partially-hybridized or fully-hybridized RFfilter with AWR electrostatic capacitance matching, Notch Tuning, andAWR Matching Adjustment.

FIG. 13 is a graph of insertion loss (attenuation) as a function offrequency showing shifting of the notch center frequency of afully-hybridized RF Pi-type filter across about a 100 MHz tuning rangewhile maintaining about a 120 MHz stopband width and at least about 30dB of attenuation.

FIG. 14 is a graph of insertion loss (attenuation) as a function offrequency showing changing of the notch depth and width for afully-hybridized RF Pi-type filter while maintaining at least about 30dB of attenuation.

FIG. 15 is a graph of insertion loss (attenuation) as a function offrequency comparing the frequency response of a partially-hybridizedPi-type RF filters using BAW, SAW, or XBAR resonators.

FIG. 16 illustrates an exemplary prior art wireless communicationenvironment comprising different wireless communication systems, and mayinclude one or more mobile wireless devices.

FIG. 17 is a more detailed block diagram of a transceiver that might beused in a wireless device, such as a cellular telephone, and which maybeneficially incorporate embodiments of the present invention forimproved performance.

Like reference numbers and designations in the various drawings indicatelike elements unless the context otherwise indicates.

DETAILED DESCRIPTION

The invention encompasses high performance radio frequency (RF) acousticwave resonator (AWR) filter circuits and methods for designing suchfilter circuits. The inventive RF filter circuits provide a high levelof attenuation at selected frequencies to eliminate unwanted RFtransmission (Tx) noise/leakage without necessarily decreasing Tx powerand/or restricting resource allocation in the Tx band. Embodimentsinclude flexible notch filtering solutions that can be optimized and/orreconfigured for different bands and combinations or aggregations ofbands, or for different telecommunication system operators in differentregions.

Acoustic Wave Resonators as Filter Components

An RF filter is a component or circuit configured to pass some radiofrequencies with relatively low signal loss and to block orsubstantially attenuate other radio frequencies. The range offrequencies passed by a filter is the “passband”. An RF filter passbandfor a particular application may be defined as a frequency range wherethe insertion loss (IL) of the filter is less than a specified valuesuch, as 1 dB or 3 dB. The range of frequencies stopped by a filter isthe “stopband” or “notch” band. An RF filter stopband for a particularapplication may be defined as a frequency range where the rejection ofthe filter is more than a specified value, such as 25 dB or 30 dB. Atypical RF filter has at least one passband and at least one stopband.

RF filters for present communication systems commonly incorporate one ormore acoustic wave resonators, including surface acoustic wave (SAW)resonators, bulk acoustic wave (BAW) resonators, film bulk acousticresonators (FBAR), and transversely-excited film bulk acousticresonators (XBAR). FIG. 2 is a diagram of a common symbol 202 for aprior art acoustic wave resonator (AWR) and the equivalent circuit model204 for an AWR. The equivalent circuit model 204 (known as theButterworth Van Dyke model) includes an inductor Lm, a capacitor Cm, anda resistor Rm coupled in series and representing the motional (acoustic)characteristics of an AWR near a resonance point, while a bracketingparallel capacitor C0 represents the electrostatic plate capacitance ofthe AWR (noting that an AWR physically comprises two electrodesstructures separated by a dielectric). C0 values are typically chosensuch that their reactance, 1/(2π×f×C0) is in the general range of about50 ohms. For each AWR, Cm will be related to C0 by: Cm=8×k_(eff)²×C0/π², where k_(eff) ² is the effective electromechanical couplingcoefficient of the AWR and depends on the material properties used tofabricate the AWR. Therefore, Cm is smaller than C0, while Lm, whichresonates with Cm at the resonance frequency, tends to be quite large.AWR equivalent elements C0, Lm, Cm, and Rm have some effect at allfrequencies, but their combined behavior results in a resonance and ananti-resonance. Accordingly, at frequencies well below and well abovethe resonance and anti-resonance frequencies, the Lm, Rm, Cm series armwill look like an open circuit (at low frequencies, Cm has highimpedance, while at high frequencies, Lm has high impedance), making theoverall circuit behave as C0 alone.

Note that when it is stated in this disclosure that a circuit creates aresonance with C0, there may be some residual inductance or capacitancefrom the acoustic branch of the AWR at the desired frequency. Forexample, at a desired passband frequency f_(P) higher than the resonancefrequency fr and antiresonance frequency fa of the AWR, the susceptanceB_(P) of a parallel-arm AWR is slightly less than the susceptance B_(C0)attributable to just C0 (noting also that the resonance frequency fr andantiresonance frequency fa of the AWR will both be spaced above or belowthe desired passband frequency f_(P), as explained below). The value ofan inductance L needed to tune out B_(P) (L=1/[2π×f_(P)×B_(P)]) thusneeds to be slightly larger than the value of an inductance needed totune out the susceptance B_(C0) attributable to just C0; however, thedifference is slight, typically a few percent. Conversely, if f_(P) islower than fr and fa, then the value of an inductance L needed to tuneout B_(P) (L=1/[2π×f_(P)×B_(P)]) would need to be slightly smaller. Asimilar argument applies to the dual case of a series inductance Ltuning out the reactance of a series-arm AWR with a similar result.Thus, while “C0” is used in this disclosure to denote the value withrespect to achieving resonance with other circuits, the actual valuewith which other circuits must resonate may be the actual value of C0 inparallel with such residual acoustic reactance. Of note, the element C0alone is a good approximate representation of an entire AWR atfrequencies sufficiently displaced from the desired notch frequency.

Acoustic wave resonators may be fabricated using conventional integratedcircuit manufacturing techniques and with different frequencycharacteristics. For example, FIG. 3 is a graph 300 of the impedance oftwo prior art ideal AWRs as a function of frequency. Graph curve 302shows that a first AWR has a resonance frequency (lowest impedance) atabout 2.80 GHz and an anti-resonance frequency (highest impedance) atabout 3.00 GHz. Graph curve 304 shows that a second AWR has a resonancefrequency at about 3.04 GHz and an anti-resonance frequency at about3.20 GHz.

A figure of merit (FOM) parameter for an AWR may be defined asFOM=k_(eff) ²×Q, where k_(eff) ² is the effective electromechanicalcoupling coefficient and Q is the quality factor. A larger value fork_(eff) ² gives a wider bandwidth, which is quite desirable at someoperational frequencies (e.g., the mid-band 5G frequencies from 2.5-3.7GHz).

Acoustic wave RF filters usually incorporate multiple AWRs. For example,an acoustic wave RF filter using the well-known “ladder” filterarchitecture generally includes at least one parallel-arm AWR (alsoknown as shunt-arm AWRs) and at least one series-arm AWR. Inconventional acoustic wave RF bandpass filter designs, a parallel-armAWR typically has a resonance frequency below the passband of the filterand an anti-resonance frequency within the passband. Conversely, aseries-arm AWR typically has a resonance frequency within the passbandof the filter and an anti-resonance frequency above the passband.

For example, referring to FIG. 3 , an acoustic wave RF filter in whichthe parallel-arm AWRs have resonance/anti-resonance curves like graphline 302 and the series-arm AWRs have resonance/anti-resonance curveslike graph line 304 will have a passband in the frequency range coveredby graph line 306. In the passband, the parallel-arm AWRs areessentially open-circuits and the series-arm AWRs are essentiallyshort-circuits. Both below and above the passband, the general level ofstopband attenuation is generally dependent on the ratio of the C0capacitances of the parallel-arm resonators to the C0 capacitances ofthe series-arm resonators, since, away from the resonance andanti-resonance frequencies, the AWR's are approximately just capacitorsand the filter circuit acts as a capacitive voltage-divider ladder.There will be two narrow notches very close to the passband—for examplein FIG. 3 , the short-circuit in curve 302 and the open-circuit of curve304 will result in narrow notches at about 2.80 GHz and 3.20 GHz,respectively. These notches are not controllable independently of thebandpass characteristic. The most important limitation of this type ofbandpass filter, evident from FIG. 3 , is that the maximum availablebandwidth (graph line 306) cannot significantly exceed the separationfa−fr between the resonance frequency fr and the anti-resonancefrequency fa of the AWR's. Since fa is given by fr×sqrt[1+(8/π²)×k_(eff)²], the relative separation (fa−fr)/fr is limited to about 0.5×k_(eff)². The upper limit on fractional bandwidth for SAW resonators is about2%, for BAW resonators, about 4-5% (even with dopants that increasek_(eff) ²), and for XBAR resonators, about 10%.

Notably, away from their resonance and anti-resonance frequencies, allacoustic wave resonators are a good approximation of simpleelectrostatic capacitors. Embodiments of the present invention utilizethis attribute to essentially de-couple the design of the stopband ornotch characteristics of an RF filter from the passband characteristicsof the RF filter.

AWR Building Blocks for RF Filters

FIG. 4 is a schematic diagram of a simple series-arm AWR filter buildingblock 400 in accordance with the present invention. A series-armacoustic wave resonator S_(AWR) has at least one terminal series coupledto a series-arm matching inductor L_(MS). In some cases, the inductancein the building block circuit (or “arm”) may be split between twoinductors coupled to opposite terminals of the AWR S_(AWR), as indicatedin FIG. 4 by a second series-arm matching inductor L_(MS) within adotted oval. The split inductance may be useful when building up RFfilters having more than one series-arm AWR filter building block 400coupled in series (see, for example, FIGS. 10 and 11 below). In someembodiments, the series-arm matching inductor(s) L_(MS) may beadjustable (e.g., digitally tunable inductors or DTLs). Examples ofDTL's are described in U.S. Pat. No. 9,197,194, issued on Nov. 24, 2015,entitled “Method and Apparatus for Use in Tuning Reactance in anIntegrated Circuit Device”, assigned to the assignee of the presentinvention and hereby incorporated by reference.

An important aspect of the series-arm AWR filter building block 400 isthat both the resonance frequency and the anti-resonance frequency ofthe series-arm AWR S_(AWR) are selected to be spaced apart in frequencyfrom the specified passband for a particular series-arm AWR filterbuilding block 400. For example, the series-arm AWR S_(AWR) resonanceand anti-resonance frequencies are selected to be below the specifiedpassband for a particular series-arm AWR filter building block 400 ifthe passband is to be at a higher frequency than the stopband.Conversely, the series-arm AWR S_(AWR) resonance and anti-resonancefrequencies are selected to be above the specified passband for aparticular series-arm AWR filter building block 400 if the passband isto be at a lower frequency than the stopband. This contrasts withconventional AWR bandpass filter designs in which a series-arm AWRtypically has a resonance frequency within the passband and ananti-resonance frequency above the passband. Accordingly, in embodimentsof the present invention, the passband characteristics of the series-armAWR filter building block 400 are essentially independent of its notchfiltering characteristics, as further described below.

Another important aspect of the series-arm AWR filter building block 400is that the total inductance of the coupled series-arm matchinginductor(s) L_(MS) matches the capacitance C0 of the associatedseries-arm AWR S_(AWR). “Matching” the series-arm inductor(s) L_(MS)means selecting a total inductance value that resonates with (i.e.,tunes out) the electrostatic capacitance C0 of the series-arm AWRS_(AWR) around the center frequency of a desired passband. The resultingseries-resonant LC circuit and the selection of theresonance/anti-resonance frequencies outside the passband makes theseries-arm AWR filter building block 400 behave like a short-circuitwithin the passband (L_(MS) in series resonance with C0 in S_(AWR)).

FIG. 5 is a schematic diagram of an advanced series-arm AWR filterbuilding block 500 in accordance with the present invention. Theadvanced series-arm AWR filter building block 500 starts with the simpleseries-arm AWR filter building block 400 of FIG. 4 and adds one or twooptional features.

The first optional feature in FIG. 5 is a series-arm Notch Tuningcircuit 502 that includes, in the illustrated embodiment, a series-armtuning inductor L_(TS) and a series-arm tuning capacitor C_(TS) coupledin parallel with the series-arm AWR S_(AWR). The resulting LC series-armNotch Tuning circuit 502 in parallel with the series-arm AWR S_(AWR)allows tuning of the anti-resonance frequency of the advanced series-armAWR filter building block 500 without affecting its resonance frequency.Consequently, in a complete RF filter with both series-arms andparallel-arms, the series-arm Notch Tuning circuit 502 provides theability to tune the center frequency of the notch filter characteristicsof the RF filter and/or the depth (level of attenuation) and width ofthe notch (see FIGS. 13 and 14 below for examples). Note that in someembodiments, the series-arm Notch Tuning circuit 502 may comprise onlyan adjustable series-arm tuning inductor L_(TS) or only an adjustableseries-arm tuning capacitor C_(TS).

A second optional feature is a series-arm AWR Matching Adjustmentcircuit 504 that includes a series-arm match-adjustment capacitor C_(M)scoupled between the series-arm AWR S_(AWR) and the series-arm matchinginductor L_(MS). The combination of the series-arm matching inductorL_(MS) and the series-arm match-adjustment capacitor C_(M)s provides avariable LC matching circuit that can be adjusted (in contrast to justthe fixed inductor LMS) so that the series-arm AWR filter building block500 can be made to look like a short-circuit within the passbandfrequency range. This variable LC matching circuit allows adjustment ofthe matching, which may be necessary (or at least desirable) when theNotch Tuning circuit 502 is used.

If the series-arm matching inductor L_(MS) is used alone, as in FIG. 4 ,its value is chosen so as to series-resonate the capacitance C0 of theseries-arm AWR at or near the center of the desired passband, therebymaking the series-arm AWR filter building block 400 act as ashort-circuit in the passband. If a series-arm match-adjustmentcapacitor C_(MS) is added, as in FIG. 5 , its purpose is to create,along with L_(MS), an adjustable effective inductanceL_(eff)=L_(MS)×{1−1/[(2×π×f)²×L_(MS)×C_(MS)]}. By varying the value ofcapacitor C_(MS), small adjustments may be made in the value of L_(eff),such as might be needed to maintain the short-circuit characteristic ofthe series-arm AWR filter building block 500 in the desired passbandwhen the Notch Tuning circuit 502 is used. Note that: (1) in the aboveexpression for L_(eff), if C_(MS) is set to infinity, thenL_(eff)=L_(MS), meaning that C_(M)s is effectively replaced by a shortcircuit; and (2) as C_(MS) is made smaller, L_(eff) also gets smaller,meaning that the variable range of L_(eff) lies entirely below the valueof L_(MS). It follows that in order to have L_(eff) of the advancedseries-arm AWR filter building block 500 in FIG. 5 attain the value ofthe series-arm matching inductor L_(MS) shown in FIG. 4 , the series-armmatching inductor L_(MS) in FIG. 5 must have a larger value than theseries-arm matching inductor L_(MS) in FIG. 4 .

As the name implies, the series-arm match-adjustment capacitor C_(MS) isadjustable to provide a range of fine-tuning adjustments to maintainmatching between the series-arm matching inductor L_(MS) and theelectrostatic capacitance C0 of the series-arm AWR S_(AWR). For example,adding the optional series-arm Notch Tuning circuit 502 and setting thenotch filter characteristics to desired width, depth, and/or centerfrequency values may have an effect on the matching of the series-armmatching inductor L_(MS) to the electrostatic capacitance C0 of theseries-arm AWR S_(AWR). The series-arm match-adjustment capacitor C_(M)sallows some latitude in maintaining that match when the Notch Tuningcircuit 502 is included and the series-arm tuning capacitor C_(TS) isvaried.

The series-arm match-adjustment capacitor C_(MS) may be adjusted by oneor more methods. For example, once notch tuning values are known (e.g.,by modeling or IC characterization), an IC embodiment may be adjusted byfixing a final capacitance value at the time of manufacture (e.g., byapplication of one or more mask layers to set a configuration) or duringproduction testing or by a customer (e.g., by laser trimming or“blowing” fusible links). In embodiments in which the series-armmatch-adjustment capacitor C_(MS) is a digitally tunable capacitor(DTC), adjustment may be under program control (e.g., by IC input pinsor control words, or by the use of look-up tables external or internalto an IC that includes the series match-adjustment capacitor C_(MS)) andsettable during production testing or by a customer, or dynamically setin the field in response to environmental (physical and RF)characteristics, such as temperature, transmitter power settings,receiver sensitivity, bands in use, transmission band frequency resourceblock (RB) allocation, etc. Examples of DTC's are described in U.S. Pat.No. 9,024,700, issued on May 5, 2015, entitled “Method and Apparatus foruse in Digitally Tuning a Capacitor in an Integrated Circuit Device”,assigned to the assignee of the present invention and herebyincorporated by reference.

Also shown in FIG. 5 is a position or node, L_(SPLIT) Node, at which asecond series-arm matching inductor L_(MS) may be located for particularapplications, as noted above (FIGS. 8-11 below also show an L_(SPLIT)Node for the same purpose). Note that, in general, the series order ofthe L_(MS), C_(MS), and S_(AWR) components does not matter as to theperformance of the circuit; however, if the series-arm matchinginductance L_(MS) is split into two physical inductors, the position ofthe dot marked L_(SPLIT) is a natural place to insert the second part ofL_(MS). In some cases, when the parasitic capacitance of the physicalcomponents to ground is taken into account, some orderings might performslightly better than others.

Another way of characterizing a series-arm AWR filter building blockencompassed by the present invention is as either (1) “partiallyhybridized”, meaning that the series-arm AWR S_(AWR) is coupled to theseries-arm matching inductor L_(MS), or (2) “fully hybridized”, meaningthat the series-arm AWR S_(AWR) is coupled to the series-arm matchinginductor L_(MS) and the series-arm Notch Tuning circuit 502, andoptionally coupled to the series-arm AWR Matching Adjustment circuit504. Accordingly, in both types of hybridization, an acoustic waveresonator is combined with at least one matching inductor, in contrastto conventional designs in which RF filters are generally purely LCnetworks or purely AWR networks.

FIG. 6 is a schematic diagram of a simple parallel-arm AWR filterbuilding block 600 in accordance with the present invention. Theparallel-arm AWR filter building block 600 includes a parallel-armmatching inductor L_(MP) coupled in parallel with a parallel-armacoustic wave resonator P_(AWR). The parallel-arm AWR filter buildingblock 600 may be present in multiple instances in the filter network,typically along with one or more instances of the series-arm AWR filterbuilding blocks 400 or 500 (see FIGS. 9 and 11 for examples).

An important aspect of the parallel-arm AWR filter building block 600 isthat both the resonance frequency and the anti-resonance frequency ofthe parallel-arm AWR P_(AWR) are selected to be spaced apart infrequency from the specified passband for a particular parallel-arm AWRfilter building block 600. This contrasts with conventional AWR bandpassfilter designs in which a shunt (parallel arm) AWR typically has aresonance frequency below the passband and an antiresonance frequencywithin the passband. Accordingly, in embodiments of the presentinvention, the passband characteristics of the parallel-arm AWR filterbuilding block 600 are essentially independent of its notch filteringcharacteristics, as further described below.

Another important aspect of the parallel-arm AWR filter building block600 is that the coupled parallel-arm matching inductor(s) L_(MP) matchesthe capacitance C0 of the associated parallel-arm AWR P_(AWR).“Matching” the parallel-arm matching inductor(s) L_(MP) means selectingan inductance value that resonates with (i.e., tunes out) theelectrostatic capacitance C0 of the parallel-arm AWR P_(AWR) around thecenter frequency of a desired passband. The resulting resonant LC tankcircuit and the selection of the resonance/anti-resonance frequenciesoutside the passband makes the parallel-arm AWR filter building block600 behave like an open circuit within the passband (L_(MP) in parallelresonance with C0 in P_(AWR)).

FIG. 7 is a schematic diagram of an advanced parallel-arm AWR filterbuilding block 700 in accordance with the present invention. Theadvanced parallel-arm AWR filter building block 700 starts with thesimple parallel-arm AWR filter building block 600 of FIG. 6 and adds oneor two optional features.

The first optional feature in FIG. 7 is a parallel-arm Notch Tuningcircuit 702 that includes, in the illustrated embodiment, a parallel-armtuning inductor L_(TP) and a parallel-arm tuning capacitor C_(TP)coupled in series with the parallel-arm AWR P_(AWR). The resulting LCparallel-arm Notch Tuning circuit 702 in series with the parallel-armAWR P_(AWR) allows tuning of the resonance characteristics of theadvanced parallel-arm AWR filter building block 700 without affectingits anti-resonance frequency. The series (i.e., short-circuit) AWRresonance of the parallel-arm AWR filter building block 700 contributesto the notch/stopband, and the parallel-arm Notch Tuning circuit 702adjusts the frequency that the parallel-arm AWR filter building block700 contributes to the stopband/notch of an overall filter network.Consequently, in a complete RF filter with both series-arms andparallel-arms, the parallel-arm Notch Tuning circuit 702 provides theability to tune the center frequency of the notch filter characteristicsof the RF filter and/or the depth and width of the notch (see FIGS. 13and 14 below for examples). Note that in some embodiments, theparallel-arm Notch Tuning circuit 702 may comprise only an adjustableparallel-arm tuning inductor L_(TP) or only an adjustable parallel-armtuning capacitor C_(TP).

A second optional feature is a parallel-arm AWR Matching Adjustmentcircuit 704 that includes a parallel-arm match-adjustment capacitorC_(MP) coupled in parallel with the parallel-arm AWR S_(AWR) and theparallel-arm matching inductor L_(MP). The combination of theparallel-arm matching inductor L_(MP) and the parallel-armmatch-adjustment capacitor C_(MP) provides a variable LC circuit thatcan be used to more closely match the electrostatic capacitance C0 ofthe parallel-arm AWR P_(AWR) so that the parallel-arm AWR filterbuilding block 700 looks like an open-circuit within the passbandfrequency range. The parallel-arm match-adjustment capacitor C_(MP) maybe adjusted in one or more of the ways described above for theseries-arm match-adjustment capacitor C_(MS) of FIG. 5 . Note that, ingeneral, the series order of the L_(TP), C_(TP), and P_(AWR) componentsdoes not matter as to the performance of the circuit. Again, in somecases, when the parasitic capacitance of the physical components toground is taken into account, some orderings might perform slightlybetter than others.

Analogous to the series-arm AWR Matching Adjustment circuit 504 of FIG.5 , in the parallel-arm AWR Matching Adjustment circuit 704, theparallel-arm match-adjustment capacitor C_(MP) is meant to “convert”matching inductor L_(MP) into an adjustable effective inductance L_(eff)consisting of L_(MP) and C_(MP) together. Since L_(MP) and C_(MP) are inparallel with each other (rather than in series as in FIG. 5 ), L_(eff)is given by L_(eff)=L_(MP)/{1−(2π×f)²×L_(MP)×C_(MP)}. Note that L_(eff)is greater than L_(MP) when C_(MP) is present; setting C_(MP) to zero inthis expression yields L_(eff)=L_(MP), which corresponds to the simpleparallel-arm AWR filter building block 600 in which C_(MP) is replacedby an open circuit (i.e., C_(MP) is omitted). Thus, in order to make the“effective inductance” L_(eff) encompass a value that “matches”(resonates) the capacitance C0 of the parallel-arm acoustic waveresonator P_(AWR) at or near the center of the desired stopband/notch asC_(MP) is varied upward from zero, the parallel-arm matching inductorL_(MP) must have a smaller value than the parallel-arm matching inductorL_(MP) in FIG. 6 , in which C_(MP)=“open circuit”=“zero” (i.e., C_(MP)is omitted).

Another way of characterizing a parallel-arm AWR filter building blockencompassed by the present invention is as either (1) “partiallyhybridized”, meaning that the parallel-arm AWR P_(AWR) is coupled to theparallel-arm matching inductor L_(MP), or (2) “fully hybridized”,meaning that the parallel-arm AWR P_(AWR) is coupled to the parallel-armmatching inductor L_(MP) and the parallel-arm Notch Tuning circuit 702,and optionally coupled to the parallel-arm AWR Matching Adjustmentcircuit 704.

RF Filter Architectures

The series-arm AWR filter building blocks 400, 500 and the parallel-armAWR filter building blocks 600, 700 may be combined to form a variety ofRF filter architectures. In the RF filter architecture examples below,building blocks are shown with the optional Notch Tuning and AWR MatchAdjustment circuitry of the advanced series-arm AWR filter buildingblock 500 and the advanced parallel-arm AWR filter building block 700,but it should be understood that any of the architectures may be madeusing just the simple series-arm AWR filter building block 400 and thesimple parallel-arm AWR filter building block 600. Of note, the simpleand advanced types of AWR filter building blocks 400, 500, 600, 700 maybe “mixed and matched” as desired for a particular application, althoughif an AWR Matching Adjustment circuits 504, 704 is used, it may bedesirable to implement such circuits in both the series and shunt arms.

FIG. 8 is a schematic diagram of a L-type RF filter 800 that combinesone series-arm AWR filter building block with one parallel-arm AWRfilter building block. Note that in alternative embodiments, theparallel-arm AWR filter building block may be coupled to the L_(SPLIT)Node of the series-arm AWR filter building block rather than as shown.However, depending on the exact system circuitry that precedes andfollows the L-type RF filter 800, there may be some advantage tochoosing a particular coupling point to the series-arm AWR filterbuilding block for the parallel-arm AWR filter building block over othercoupling points.

FIG. 9 is a schematic diagram of a Pi-type RF filter 900 that combinesone series-arm AWR filter building block with two bracketingparallel-arm AWR filter building blocks.

FIG. 10 is a schematic diagram of a T-type RF filter 1000 that combinestwo series-arm AWR filter building blocks with one intermediateparallel-arm AWR filter building block. A “bridged-T” type configurationwould be a variation that would include at least a capacitor coupled tothe unattached end terminals of the illustrated two series-arm AWRfilter building blocks. When a bridged-T topology is used, thecomponents in the “bridge” (i.e., the components connected directlybetween the unattached end terminals) as well as the components in thetwo series-arms AWR filter building blocks will affect more than one ofthe minima of a composite notch. Thus, while a bridged-T circuit mayallow the same flexibility in notch tuning/adjustment as the L-type,Pi-type, T-type topologies (as well as the ladder topology describedbelow), it is more difficult to determine the proper adjustments of allthe variable components in a bridged-T topology. In contrast, in thedisclosed topologies, each building block (series-arm or parallel-arm)controls exactly one of the minima in a composite notch.

The L-type, Pi-type, and T-type RF filters shown in FIGS. 8-10 arespecific circuits using 2 or 3 AWR filter building blocks, and aresimply instances of a more general “ladder” architecture having analternating series-arm/parallel-arm network topology. For example, FIG.11 is a block diagram a four-resonator “laddered” RF filter 1100 thatcombines two series-arm AWR filter building blocks 1102, 1104 (in thisexample, with Notch Tuning and AWR Match Adjustment circuitry) and twoparallel-arm AWR filter building blocks 1106, 1108 (in this example,with Notch Tuning and AWR Match Adjustment circuitry). With suitablevalues for the series-arm and parallel-arm matching inductors L_(MS),L_(MP), the illustrated RF filter 1100 may be particularly useful fordefining a sharp notch filter characteristic to protect a frequency band(e.g., the WiFi band), thereby allowing wireless operation on nearbyfrequencies without restrictions on resource block allocations andwithout requiring any (or any significant) transmission power reduction.

While FIG. 11 shows a four-resonator “laddered” RF filter 1100,additional series-arm and parallel-arm AWR filter building blocks may beadded to the “ladder” to increase the number of resonators, trading offsharper notch filtering characteristics against increased signalattenuation. Further, while FIG. 11 shows an alternatingseries-arm/parallel-arm network topology, it is also possible to placemore than one parallel-arm AWR filter building block or more than oneseries-arm AWR filter building block in immediate succession.

Other types of RF filter architectures or networks may be used with theseries-arm AWR filter building blocks and parallel-arm AWR filterbuilding blocks described above. Further, Also, one or more complete RFfilter structures may be coupled together to form a larger circuit, suchas a duplexer or diplexer.

Note that each series-arm AWR filter building block and parallel-arm AWRfilter building block in a particular RF filter architecture introducesits own resonance/anti-resonance characteristic to the RF filter. Asdescribed below, the combination of the resonance/anti-resonancecharacteristics defines the center frequency, width, and depth (level ofattenuation) of the stopband of the RF filter. It is the (open-circuit)anti-resonances of the series-arm AWR filter building blocks, and the(short-circuit) resonances of the parallel-arm AWR filter buildingblocks that contribute to the stopband.

RF Filter Design with Tuning and Matching

The inventive series-arm AWR filter building blocks 400, 500 andparallel-arm AWR filter building blocks 600, 700 essentially de-couplethe stopband or notch characteristics of an RF filter from the passbandcharacteristics of the RF filter. Accordingly, each of those de-coupledparameters can be individually designed to meet the specifications of aparticular application. Partially-hybridized or fully-hybridizedseries-arm and parallel-arm AWR filter building blocks in accordancewith the present invention can be used to build RF filters having“de-coupled” or essentially independent passband and stopbandcharacteristics. Such “de-coupled” RF filters can have (1) wideband andlow insertion loss passbands and (2) wideband deep notches (stopbands)with a specifically placed notch center frequency, without compromisingthe passband characteristics.

FIG. 12A is a process flow chart 1200 showing a summarized methodologyfor designing RF filters having essentially independent passband andstopband characteristics, and encompasses both partially-hybridized andfully-hybridized filter networks. The methodology applies to any RFfilter architecture or network using the series-arm AWR filter buildingblocks 400, 500 and parallel-arm AWR filter building blocks 600, 700described above.

A first step is to enable wide and deep notches (stopbands) by selectingAWR elements for a selected RF filter architecture having (1) resonanceand anti-resonance frequencies in the desired notch band; and (2)overall impedance levels scaled towards an “all-stop” networkconfiguration, e.g., using relatively small AWR electrostaticcapacitances C0 for the series-arm AWRs S_(AWR) and relatively large AWRelectrostatic capacitances C0 for the parallel-arm AWRs P_(AWR)[Block1202]. This helps to make the series-arm AWRs S_(AWR) better opencircuits at their antiresonance frequency and the parallel-arm AWRsP_(AWR) better short circuits at their resonance frequency. This resultsin a suitably deep notch at the desired notch frequency (displaced fromthe desired passband)—because of the good short-circuit and open-circuitbehavior of the selected AWRs having their respective electrostaticcapacitances C0 scaled low in series arms and high in parallel arms.Note that, prior to performing the next step (Block 1204), this filterstructure would behave like an “all-stop” capacitive voltage divider atfrequencies away from the notch, having somewhat high attenuation of allfrequencies, including the desired passband.

Next, enable wide passbands with low insertion loss by selecting valuesfor the series-arm matching inductor L_(MS) and the parallel-armmatching inductor L_(MP) to resonate respectively with the correspondingelectrostatic capacitance C0 of the series-arm AWR S_(AWR) and theparallel-arm AWR P_(AWR) within the selected passband [Block 1204].Thus, at the selected passband frequencies, the RF filter behaves nearlylike a direct wire connection from input to output. At these passbandfrequencies, displaced from the notch frequencies, the AWR's themselvesare (to a good approximation) acting as just electrostatic capacitorswithout mechanically-generated resonances, so that the matchinginductors, resonating with the electrostatic capacitances of the AWRs,render series-arms as short circuits and parallel arms as open circuits.The insertion loss and bandwidth of the passband is determined by theinductance values and the Q factor of the matching inductors L_(MS),L_(MP).

Optionally, tune the notches in frequency/width/depth using theseries-arm and parallel-arm Notch Tuning circuits (e.g., a DTC) [Block1206]. Examples of such tuning are given below.

Optionally, tune the matching characteristics with respect to theelectrostatic capacitances C0 in the series-arm AWR S_(AWR) and theparallel-arm AWR P_(AWR) using corresponding AWR Matching Adjustmentcircuits (e.g., DTCs) [Block 1208]. If this option is elected, therebyinserting variable capacitors C_(MS) and/or C_(MP), then for a specifiedpassband and stopband the appropriate value of the matching inductorsL_(MS) and/or L_(MP) will be different (that is, a larger L_(MS) and/orsmaller L_(MP) will be needed) than would have been appropriate had thisoption not been elected.

FIG. 12B is a process flow chart 1250 showing a detailed methodology fordesigning a particular partially-hybridized or fully-hybridized RFfilter with AWR electrostatic capacitance matching, Notch Tuning, andAWR Matching Adjustment. The process includes:

Block 1252: Specify requirements for notch center-frequency/width/depth(attenuation) and passband (PB) range and insertion loss (IL). Thespecification may be a function of a requirement of a standards body orof a customer.

Block 1254: Select AWRs with “notch frequencies” (i.e., anti-resonancefrequencies for series-arm resonators and resonance frequencies forparallel-arm resonators) in the desired notch band and thus spaced fromthe passband, and then scale the electrostatic capacitances C0 of theseries-arm resonators to be smaller than that of parallel-arm resonatorsto ensure wide and/or deep notches. Note: if the tuning option (Block1206) is not to be elected, ensure that the notch-frequencies of theAWR's fully span the desired notch band.

Block 1256: For each AWR, determine an inductor value for the matchinginductor L that provides an acceptably low IL over the specified PBrange. The value should resonate with the electrostatic capacitance C0in the corresponding AWR at the center frequency of the passband.

Block 1258: Query: Does the notch require tuning?

Block 1260: If the notch does not require tuning, then the design iscomplete (done).

Block 1262: If the notch does require tuning, then specify a tuningrange and include Notch Tuning circuits for each AWR.

Block 1264: For each AWR, determine Notch Tuning circuit LC values thatare resonant at the center frequency of the notch tuning range. Byselecting L and C values that self-resonate in the center of the notchtuning range, they are essentially “neutral” (i.e., do not move theAWR's notch-frequency) when thus “center-tuned”. Then, per Block 1266,the notch-frequency of each AWR can be tuned lower or higher by settingthe variable capacitor larger or smaller, respectively.

Block 1266: For each AWR's Notch Tuning circuit, fix the L value andselect a sequence of C values that tune the AWR's notch-minimum over thedesired range.

Block 1268: Query: Does the PB IL remain sufficiently low at allpassband frequencies as the notch is tuned across the desired stopbandrange?

Block 1270: If the PB IL is sufficiently low after the notch is tuned,then the design is complete (done).

Block 1272: If the PB IL is not sufficiently low after the notch istuned, then add an AWR Matching Adjustment circuits and adjust theresulting matching LC circuit until it resonates with the electrostaticcapacitance C0 of the corresponding AWR around the center frequency ofthe passband. Again, if these LC match-adjustment circuits are added,the values of the series-arm matching inductor L_(MS) and theparallel-arm matching inductor L_(MP) will be different from the valuesspecified in Block 1256. That is, a larger L_(MS) and/or smaller L_(MP)will be needed for the specified passband and stopband so that, at ornear the center of the passband, the effective inductance of the LCcircuit will be approximately equal to the inductance values specifiedin Block 1256.

Block 1274: For each AWR's LC notch tuning circuit, fix the L value andupdate the C values that re-tune that AWR's notch-minimum over thedesired range.

Block 1276: At each notch frequency thus tuned, adjust the variablecapacitor of the AWR Matching Adjustment circuit so as to obtain(“re-establish”) a low (preferably the lowest) insertion loss over thePB.

Block 1278: The design is complete (done).

As a practical matter, a designer may choose a partially hybridized or afully hybridized design as a goal, and thus a number of the steps inFIG. 12B may be skipped over or omitted. For example, if it is known inadvance whether or not tuning adjustments will be needed and used, thenthe “updating” steps may not be needed. More generally, it should bekept in mind that, for a partially hybridized filter design withouttuning and a fully hybridized filter design with tuning and matchingadjustment intended for the same application (passband and stopbandfrequencies), the values of L_(MS) and L_(MP) would be different in thetwo designs. In the fully hybridized design with matching adjustment,L_(MS) would have a larger value and L_(MP) would have a smaller valuecompared to the values of the corresponding L_(MS) and L_(MP) componentsin the partially hybridized design. Each L and variable C adjustablematching circuit in the fully hybridized design is meant to look like avariable inductor having an adjustable effective inductance L_(eff) in arange around the fixed values of L_(MS) and L_(MP) in the correspondingpartially-hybridized design.

Tuning Examples

The center frequency, width, and depth of an RF filter notch inaccordance with the present invention is initially determined by theselection of RF filter architecture and the specific AWR components forthe series-arm AWRs S_(AWR) and the parallel-arm AWRs P_(AWR). Thus, theresonance/anti-resonance characteristics of a first set of three AWRs ina Pi-type filter generally produce a “composite” notch with 3 minima anda particular center frequency. For example, the first set of three AWRsmay result in a “wide and shallow” notch having a notch 70 MHz wide atan attenuation level of about 30 dB. For a second first set of threeAWRs with different resonance/anti-resonance characteristics, the centerfrequency may shift up or down in frequency and/or the width and depthof the notch may differ from the first set of three AWRs. For example,the second set of three AWRs may result in a “deep and narrow” notchhaving a notch 20 MHz wide at an attenuation level of about 75 dB. Thus,a particular set of RF filter characteristics can be achieved byselecting more closely-spaced or more widely-spaced “notch frequencies”(meaning anti-resonance frequency in the series arm, and resonancefrequency in the parallel arm) among the resonators. Eitherpartially-hybridized or fully-hybridized series-arm and parallel-arm AWRfilter building blocks can be used, but a partially-hybridized designwill not be tunable.

As noted above, in a fully-hybridized RF filter, tuning circuits areadded to enable tuning of the composite AWR minima with respect tocenter frequency, width, and depth, as long as the resulting insertionloss versus frequency curve meets a specified attenuation-levelrequirement with respect to its width and has an appropriate centerfrequency. For example, a set of three AWR's having notch frequenciesspaced apart may be selected so as to produce a certain (probablyintermediate) notch depth and width. The notch tuning circuits on thethree resonators may then be used to move the “notch frequencies” closertogether or farther apart.

FIG. 13 is a graph 1300 of insertion loss (attenuation) as a function offrequency showing shifting of the notch center frequency of afully-hybridized RF Pi-type filter across about a 100 MHz tuning rangewhile maintaining about a 120 MHz stopband width and at least about 30dB of attenuation. As a Pi-type filter, the RF filter includes oneseries-arm AWR filter building block and two bracketing parallel-arm AWRfilter building blocks (see FIG. 9 ), and accordingly combines threeresonance/anti-resonance AWR characteristics.

Graph line 1302 represents the result of a first set of tuning valuesprovided by the Notch Tuning circuits of the RF filter, emphasizingnotch center frequency. Graph line 1302 has three minima, two “flyback”lobes between the outer minima, a center frequency of about 2.40 GHz,and a width of about 110 MHz at the 30 dB level of attenuation. Graphline 1304 represents the result of a second set of tuning valuesprovided by the Notch Tuning circuits of the RF filter, showing a shiftof the center frequency downward to about 2.34 GHz while maintaining awidth of about 110 MHz at the 30 dB level of attenuation (although theflyback lobes are closer to the 30 dB level than for graph line 1302).Graph line 1306 represents the result of a third set of tuning valuesprovided by the Notch Tuning circuits of the RF filter, showing afurther shift of the center frequency downward to about 2.30 GHz whilemaintaining a width of about 110 MHz at the 30 dB level of attenuation(although one of the flyback lobes is even closer to the 30 dB levelthan for graph line 1304). Notably, for all three sets of tuning values,the passband from about 2.50 GHz to about 2.70 GHz has a very flatresponse and wide bandwidth. The bandwidth and spacing of the passbandfrom the notch are larger than would typically be supported by the AWRby itself. The resulting filter has a response that have essentially“de-coupled” or independent passband and stopband characteristicswithout some of the constraints imposed by the k_(eff) ² parameter ofthe AWR.

Thus, in the example shown in FIG. 13 , the −1 dB bandwidth of thepassband is at least 200 MHz centered at about 2.6 GHz, which is atleast 7.7% fractional bandwidth. In contrast, a conventional prior artbandpass filter using the same AWR material used in these simulations(having a k_(eff) ² of 0.09) could support a passband fractionalbandwidth of only about 4×k_(eff) ²/π²=3.6% if the resonators wereconfigured as shown in FIG. 3 . In FIG. 13 , the passband fractionalbandwidth of at least 7.7%—more than twice that of a conventionaldesign—is a property of the resonator capacitances C0 and the matchinginductors L_(MS), L_(MP), and is not limited as in the conventionalprior art bandpass filter paradigm.

FIG. 14 is a graph 1400 of insertion loss (attenuation) as a function offrequency showing changing of the notch depth and width for afully-hybridized RF Pi-type filter while holding at least 30 dB ofattenuation. In this example, a set of three AWR's having notchfrequencies spaced apart have been selected so as to produce anintermediate notch depth and width. Graph line 1402 represents theresult of these selected “pre-tuning” values, with a center frequency ofabout 2.37 GHz, a notch width of about 75 MHz wide at the 40 dB level ofattenuation and about 85 MHz at the 30 dB level of attenuation, threeminima, and two “flyback” lobes between the outer minima. Graph line1404 represents the result of a first set of tuning values provided bythe Notch Tuning circuits of the RF filter, emphasizing notch width overdepth. Graph line 1404 has a center frequency of about 2.37 GHz and anotch width of about 100 MHz at the 30 dB level of attenuation. Graphline 1406 represents the result of a second set of tuning valuesprovided by the Notch Tuning circuits of the RF filter, emphasizingnotch depth over width. Graph line 1406 has a center frequency of about2.365 GHz, a notch width of about 50 MHz at about the 60 dB level ofattenuation and about 70 MHz at the 30 dB level of attenuation. Whilenot shown in FIG. 14 , the passband from about 2.50 GHz to about 2.70GHz has a very flat response and wide bandwidth for all three sets oftuning values.

Micro-Level Tuning Capability

An additional aspect of embodiments of the present invention thatincorporate DTCs in Notch Tuning circuits and/or AWR Matching Adjustmentcircuits is a “micro-level tuning” capability. Such embodiments may havetheir tuning parameters defined during production testing or by acustomer on a one-time basis (e.g., to configure a transceiver for thewireless standards in a particular region or of a particular operator).However, in DTC-based embodiments of the Notch Tuning circuits and/orAWR Matching Adjustment circuits, adjustments may be under programcontrol and thus settable dynamically in response to environmental(physical and RF) factors, such as temperature, changing transmissionleakage characteristics, transmitter power settings, receiversensitivity, bands in use, etc.

For example, transmission leakage characteristics may change dependingon how a resource block allocation is configured, such as contiguous vs.non-contiguous resource block allocation, the bandwidth of the resourceblock allocation, and the offset of resource block allocation positionsfrom the band edge (e.g., the lower frequency band edge of n41 in thecase of n41 and n40/n30/Wi-Fi coexistence). As another example, theintermodulation distortion (IMD) order dominating the transmissioninterference/leakage may change dynamically along with the behavior ofany particular intermodulation distortion order itself. For instance, inthe 5G n41 band, the 5^(th)-order IMD for bandwidths of 50-100 MHz, andthe 3^(rd)-order IMD for bandwidths of 100 MHz, may fall within the n40band and violate a co-existence requirement set by a standards body(e.g., the 3rd Generation Partnership Project). There may also be caseswhere a filter would need to be adjusted as a result of carrieraggregation configurations or simply for a wideband filter that can beadjusted to accommodate different selected bands at different times(e.g., a reconfigurable filter). Accordingly, it may be useful tomicro-level tune the center frequency, width, and/or depth of a notch,and/or micro-level tune the matching of a matching inductor L_(MS),L_(MP) to respond to such varying factors in real time.

Scaling with AWR Technology

A benefit of embodiments of the present invention is that the inventivehybrid filter architectures can be applied to any AWR technology. Byde-coupling the stopband or notch characteristics of an RF filter fromthe passband characteristics of the RF filter (by hybridizing anacoustic wave resonator S_(AWR), P_(AWR) with a matching inductor thatresonates with the associated capacitance C0 of the AWR), filterperformance scales with the bandwidth capability of the AWR without someof the constraints imposed by the k_(eff) ² parameter of the AWR. Afurther notable advantageous result is that wider and deeper notches inembodiments of the invention become possible as the k_(eff) ² parameterof an individual resonator increases.

For example, FIG. 15 is a graph 1500 of insertion loss (attenuation) asa function of frequency comparing the frequency response of apartially-hybridized Pi-type RF filters using BAW, SAW, or XBARresonators. The RF filters included a matching inductor L_(MS) for theseries-arm AWR S_(AWR) and corresponding matching inductors L_(MP) forthe two parallel-arm AWRs P_(AWR), but did not include Notch Tuningcircuits or AWR Matching Adjustment circuits.

Graph line 1502 represents use of SAW AWRs (k_(eff) ²≈0.044) in theseries-arm and parallel-arms of the RF filter. Graph line 1504represents use of BAW AWRs (k_(eff) ²≈0.09) in the series-arm andparallel-arms of the RF filter. Graph line 1506 represents use of XBARAWRs (k_(eff) ²≈0.20) in the series-arm and parallel-arms of the RFfilter. As graph line 1506 indicates, use of XBAR AWRs allows a verywide initial notch with flyback maintained well below 30 dB.

In addition, the use of matching inductor L_(MS), L_(MP) results in verylow insertion loss in the passband (2.5-2.7 GHz) even though the AWRresonance/anti-resonance impedances are selected or scaled towards“all-stop” levels to get good notch depth. The passband may also be abit wider and flatter with higher values of k_(eff) ², but that effectis not as dramatic as the effect of higher values of k_(e)f on thestopband.

Comparison to Conventional (Pure AWR or Pure LC) Filters

By de-coupling individual AWR characteristics from passband bandwidth,embodiments of the present invention exceed the capabilities of purelyAWR RF filters using any kind of resonators (e.g., SAW, BAW, XBAR), aswell as the capabilities of purely LC RF filters. TABLE 1 belowsummarizes important differences in such conventional RF filterscompared to partially-hybridized and fully-hybridized embodiments of thepresent invention.

TABLE 1 Topology Characteristics Remarks Pure LC Resonator Q's too lowfor Cannot have both a low-loss a steep, narrow transition passband anda deep stopband between stopband and close enough to each other forpassband most applications Pure AWR In general, a tradeoff Thefractional bandwidth of the between passband IL and passband cannotexceed about notch depth & width 0.5 × k_(eff) ² (typically a few(passband width is percent) when using a traditional dependent onparameter band-pass ladder topology with k_(eff) ²) resonators designedas in FIG. 3. If, instead, AWR's are used without L's to attempt anindependent passband and stopband according to the present invention, adeep notch and low-loss passband cannot be achieved simultaneously. Deepnotch requires “all-stop” C0 scaling, but low-IL passband requires theopposite (“all-pass”) C0 scaling. Partially Low IL passband and Matchingcircuits allow building Hybridized deep/wide notches of a wide-bandpassband with (passband width is low IL; notch frequency, depth,independent of parameter and width are independently k_(eff) ²)controlled by the selection of AWRs with resonance/anti- resonancefrequencies spaced apart from passband and by AWR center frequencyspacing. Fully Partially Hybridized Allows fine tuning of hybridizedHybridized characteristics plus filter and allows micro-level tunablenotches tuning in some embodiments. (frequency, depth, width)

System Aspects

Embodiments of the present invention are useful in a wide variety oflarger radio frequency (RF) circuits and systems, including radiosystems, cellular telephones, personal computers, tablet computers,wireless network components, televisions, cable system “set top” boxes,automobile communication systems, wireless sensing devices, radarsystems, and test equipment. Further, performance enhancements to the RFfilters in a transmitter, receiver, or transceiver can have broad impactto system performance. Improvements in RF filters can enable systemperformance improvements such as longer battery life, higher data rates,greater network capacity, lower cost, enhanced security, higherreliability, etc. These improvements can be realized at many levels ofan RF system both separately and in combination, for example at the RFcircuit, RF module, mobile or fixed sub-system, or network levels.

Radio system usage includes wireless RF systems (including basestations, relay stations, and hand-held transceivers) that use varioustechnologies and protocols, including various types of orthogonalfrequency-division multiplexing (“OFDM”), quadrature amplitudemodulation (“QAM”), Code-Division Multiple Access (“CDMA”),Time-Division Multiple Access (“TDMA”), Wide Band Code Division MultipleAccess (“W-CDMA”), Global System for Mobile Communications (“GSM”), LongTerm Evolution (“LTE”), 5G, and WiFi (e.g., 802.11a, b, g, ac, ax), aswell as other radio communication standards and protocols.

As an example of wireless RF system usage, FIG. 16 illustrates anexemplary prior art wireless communication environment 1600 comprisingdifferent wireless communication systems 1602 and 1604, and may includeone or more mobile wireless devices 1606.

A wireless device 1606 may be capable of communicating with multiplewireless communication systems 1602, 1604 using one or more of thetelecommunication protocols noted above. A wireless device 1606 also maybe capable of communicating with one or more satellites 1608, such asnavigation satellites (e.g., GPS) and/or telecommunication satellites.The wireless device 1606 may be equipped with multiple antennas,externally and/or internally, for operation on different frequenciesand/or to provide diversity against deleterious path effects such asfading and multi-path interference. A wireless device 1606 may be acellular phone, a personal digital assistant (PDA), a wireless-enabledcomputer or tablet, or some other wireless communication unit or device.A wireless device 1606 may also be referred to as a mobile station, userequipment, an access terminal, or some other terminology.

The wireless system 1602 may be, for example, a CDMA-based system thatincludes one or more base station transceivers (BSTs) 1610 and at leastone switching center (SC) 1612. Each BST 1610 provides over-the-air RFcommunication for wireless devices 1606 within its coverage area. The SC1612 couples to one or more BSTs in the wireless system 1602 andprovides coordination and control for those BSTs.

The wireless system 1604 may be, for example, a TDMA-based system thatincludes one or more transceiver nodes 1614 and a network center (NC)1616. Each transceiver node 1614 provides over-the-air RF communicationfor wireless devices 1606 within its coverage area. The NC 1616 couplesto one or more transceiver nodes 1614 in the wireless system 1604 andprovides coordination and control for those transceiver nodes 1614.

In general, each BST 1610 and transceiver node 1614 is a fixed stationthat provides communication coverage for wireless devices 1606, and mayalso be referred to as base stations or some other terminology. The SC1612 and the NC 1616 are network entities that provide coordination andcontrol for the base stations and may also be referred to by otherterminologies.

An important aspect of any wireless system, including the systems shownin FIG. 16 , is in the details of how the component elements of thesystem perform. FIG. 1 is a simplified block diagram of a transceiver100. However, FIG. 17 is a more detailed block diagram of a transceiver1700 that might be used in a wireless device, such as a cellulartelephone, and which may beneficially incorporate embodiments of thepresent invention for improved performance. As illustrated, thetransceiver 1700 includes a mix of RF analog circuitry for directlyconveying and/or transforming signals on an RF signal path, non-RFanalog circuitry for operational needs outside of the RF signal path(e.g., for bias voltages and switching signals), and digital circuitryfor control and user interface requirements. In this example, a receiverpath Rx includes RF Front End, IF Block, Back-End, and Baseband sections(noting that in some implementations, the differentiation betweensections may be different). The transceiver 1700 may comprise discretecomponents and/or one or more integrated circuits within a module and/oron a circuit board, or may be fully integrated into a single integratedcircuit.

The receiver path Rx receives over-the-air RF signals through an antenna1702 and a switching unit 1704, which may be implemented with activeswitching devices (e.g., field effect transistors or FETs, particularlyMOSFETs), or with passive devices that implement frequency-domainmultiplexing, such as a diplexer or duplexer. An RF filter 1706 passesdesired received RF signals to a low noise amplifier (LNA) 1708, theoutput of which is combined in a mixer 1710 with the output of a firstlocal oscillator 1712 to produce an intermediate frequency (IF) signal.The RF filter 1706 may include one or more partially-hybridized orfully-hybridized RF filters in accordance the present invention.

The IF signal may be amplified by an IF amplifier 1714 and subjected toan IF filter 1716 before being applied to a demodulator 1718, which maybe coupled to a second local oscillator 1720. The IF amplifier 1714 mayinclude one or more partially-hybridized or fully-hybridized RF filtersin accordance the present invention. The demodulated output of thedemodulator 1718 is transformed to a digital signal by ananalog-to-digital converter 1722 and provided to one or more systemcomponents 1724 (e.g., a video graphics circuit, a sound circuit, memorydevices, etc.). The converted digital signal may represent, for example,video or still images, sounds, or symbols, such as text or othercharacters.

In the illustrated example, a transmitter path Tx includes Baseband,Back-End, IF Block, and RF Front End sections (again, in someimplementations, the differentiation between sections may be different).Digital data from one or more system components 1724 is transformed toan analog signal by a digital-to-analog converter 1726, the output ofwhich is applied to a modulator 1728, which also may be coupled to thesecond local oscillator 1720. The modulated output of the modulator 1728may be subjected to an IF filter 1730 before being amplified by an IFamplifier 1732. The IF filter 1730 may include one or morepartially-hybridized or fully-hybridized RF filters in accordance thepresent invention. The output of the IF amplifier 1732 is then combinedin a mixer 1734 with the output of the first local oscillator 1712 toproduce an RF signal. The RF signal may be amplified by a driver 1736,the output of which is applied to a power amplifier (PA) 1738. Theamplified RF signal may be coupled to an RF filter 1740, the output ofwhich is coupled to the antenna 1702 through the switching unit 1704.The RF filter 1740 may include one or more partially-hybridized orfully-hybridized RF filters in accordance the present invention.

The operation of the transceiver 1700 is controlled by a microprocessor1742 in known fashion, which interacts with system control components(e.g., user interfaces, memory/storage devices, application programs,operating system software, power control, etc.). In addition, thetransceiver 1700 will generally include other circuitry, such as biascircuitry 1746 (which may be distributed throughout the transceiver 1700in proximity to transistor devices), electro-static discharge (ESD)protection circuits, testing circuits (not shown), factory programminginterfaces (not shown), etc.

In modern transceivers, there are often more than one receiver path Rxand transmitter path Tx, for example, to accommodate multiplefrequencies and/or signaling modalities. Further, as should be apparentto one of ordinary skill in the art, some components of the transceiver1700 may be in a positioned in a different order (e.g., the filters) oromitted. Other components can be (and often are) added (e.g., additionalfilters, impedance matching networks, variable phaseshifters/attenuators, power dividers, etc.).

In order to comply with increasingly stringent system standards andcustomer requirements relating to rejection of RF interference, powerconsumption, and general efficiency and effectiveness, the currentinvention is critical to the overall solution shown in FIG. 17 . Thecurrent invention therefore specifically includes a system-levelembodiment that is enabled by inclusion in that system of embodiments inaccordance with the above disclosure and with the claims set forthbelow.

Methods

Another aspect of the invention includes methods for making a radiofrequency filter circuit based on a plurality of acoustic waveresonators (AWRs) and having a passband and a notch band. For example,one such method may include: selecting a series-arm AWR having anelectrostatic capacitance C0 small enough to be compatible with adesired stopband depth and a resonance frequency and an anti-resonancefrequency spaced apart in frequency from a desired passband; selecting aparallel-arm AWR having an electrostatic capacitance C0 large enough tobe compatible with the desired stopband depth and a resonance frequencyand an anti-resonance frequency spaced apart in frequency from thedesired passband; coupling the parallel-arm AWR in a shunt configurationwith the series-arm AWR; tuning out the electrostatic capacitance C0 ofthe series-arm AWR within the desired passband; and tuning out theelectrostatic capacitance C0 of the parallel-arm AWR within the desiredpassband, wherein the series-arm AWR anti-resonance frequencies and theparallel-arm AWR resonance frequencies define a notch band for the radiofrequency filter circuit.

Another such method may include: selecting a series-arm AWR having anelectrostatic capacitance C0 small enough to be compatible with adesired stopband depth and a resonance frequency and an anti-resonancefrequency spaced apart in frequency from the passband; coupling aseries-arm matching inductor in series with the series-arm AWR, theseries-arm matching inductor having an inductance value that resonateswith the electrostatic capacitance C0 of the series-arm AWR within thepassband; selecting a parallel-arm AWR having an electrostaticcapacitance C0 large enough to be compatible with the desired stopbanddepth and a resonance frequency and an anti-resonance frequency spacedapart in frequency from the passband; coupling a parallel-arm matchinginductor in parallel with the parallel-arm AWR, the parallel-armmatching inductor having an inductance value that resonates with theelectrostatic capacitance C0 of the parallel-arm AWR within thepassband; and coupling the parallel-arm AWR in a shunt configurationwith the series-arm AWR; wherein the series-arm AWR and the parallel-armAWR resonance frequencies and the anti-resonance frequencies define thenotch band for the radio frequency filter circuit.

Additional aspects of the above methods may include one or more of thefollowing: coupling a series-arm notch tuning circuit in parallel withthe series-arm AWR for tuning at least one of a notch band centerfrequency, a notch band width, and/or a notch band depth of the radiofrequency filter circuit; coupling a parallel-arm notch tuning circuitin series with the parallel-arm AWR for tuning at least one of a notchband center frequency, a notch band width, and/or a notch band depth ofthe radio frequency filter circuit; coupling a series-arm notch tuningcircuit in parallel with the series-arm AWR and coupling a parallel-armnotch tuning circuit in series with the parallel-arm AWR, for tuning atleast one of a notch band center frequency, a notch band width, and/or anotch band depth of the radio frequency filter circuit; coupling aseries-arm AWR matching adjustment circuit in series with the series-armAWR and the series-arm matching inductor for adjusting the resonance ofthe series-arm matching inductor with the electrostatic capacitance C0of the series-arm AWR within the desired passband; coupling aparallel-arm AWR matching adjustment circuit in parallel with theparallel-arm AWR and the parallel-arm matching inductor for adjustingthe resonance of the parallel-arm matching inductor with theelectrostatic capacitance C0 of the parallel-arm AWR within the desiredpassband; coupling a series-arm AWR matching adjustment circuit inseries with the series-arm AWR and the series-arm matching inductor, andcoupling a parallel-arm AWR matching adjustment circuit in parallel withthe parallel-arm AWR and the parallel-arm matching inductor, foradjusting the resonance of the respective coupled matching inductor withthe electrostatic capacitance C0 of the coupled AWR within the desiredpassband.

Fabrication Technologies & Options

It should be appreciated that RF filters embodying one or more of thecircuit architectures encompassed by the present invention may befabricated using conventional integrated circuit (IC) manufacturingtechniques, and that ICs embodying such RF filters may includeadditional active and passive components. For example, any of the RFfilters disclosed above may be integrated in whole or in part on thesame IC die as an RF switching unit and/or an LNA (“in part” meaningthat some components of the RF filters may be off-die).

The term “MOSFET”, as used in this disclosure, includes any field effecttransistor (FET) having an insulated gate whose voltage determines theconductivity of the transistor, and encompasses insulated gates having ametal or metal-like, insulator, and/or semiconductor structure. Theterms “metal” or “metal-like” include at least one electricallyconductive material (such as aluminum, copper, or other metal, or highlydoped polysilicon, graphene, or other electrical conductor), “insulator”includes at least one insulating material (such as silicon oxide orother dielectric material), and “semiconductor” includes at least onesemiconductor material.

As used in this disclosure, the term “radio frequency” (RF) refers to arate of oscillation in the range of about 3 kHz to about 300 GHz. Thisterm also includes the frequencies used in wireless communicationsystems. An RF frequency may be the frequency of an electromagnetic waveor of an alternating voltage or current in a circuit.

Various embodiments of the invention can be implemented to meet a widevariety of specifications. Unless otherwise noted above, selection ofsuitable component values is a matter of design choice. Variousembodiments of the invention may be implemented in any suitableintegrated circuit (IC) technology (including but not limited to MOSFETstructures), or in hybrid or discrete circuit forms. Integrated circuitembodiments may be fabricated using any suitable substrates andprocesses, including but not limited to standard bulk silicon,high-resistivity bulk CMOS, silicon-on-insulator (SOI), andsilicon-on-sapphire (SOS). Unless otherwise noted above, embodiments ofthe invention may be implemented in other transistor technologies suchas bipolar, BiCMOS, LDMOS, BCD, GaAs HBT, GaN HEMT, GaAs pHEMT, andMESFET technologies. However, embodiments of the invention areparticularly useful when fabricated using an SOI or SOS based process,or when fabricated with processes having similar characteristics.Fabrication in CMOS using SOI or SOS processes enables circuits with lowpower consumption, the ability to withstand high power signals duringoperation due to FET stacking, good linearity, and high frequencyoperation (i.e., radio frequencies up to and exceeding 300 GHz).Monolithic IC implementation is particularly useful since parasiticcapacitances generally can be kept low (or at a minimum, kept uniformacross all units, permitting them to be compensated) by careful design.

Voltage levels may be adjusted, and/or voltage and/or logic signalpolarities reversed, depending on a particular specification and/orimplementing technology (e.g., NMOS, PMOS, or CMOS, and enhancement modeor depletion mode transistor devices). Component voltage, current, andpower handling capabilities may be adapted as needed, for example, byadjusting device sizes, serially “stacking” components (particularlyFETs) to withstand greater voltages, and/or using multiple components inparallel to handle greater currents. Additional circuit components maybe added to enhance the capabilities of the disclosed circuits and/or toprovide additional functionality without significantly altering thefunctionality of the disclosed circuits.

Circuits and devices in accordance with the present invention may beused alone or in combination with other components, circuits, anddevices. Embodiments of the present invention may be fabricated asintegrated circuits (ICs), which may be encased in IC packages and/or inmodules for ease of handling, manufacture, and/or improved performance.In particular, IC embodiments of this invention are often used inmodules in which one or more of such ICs are combined with other circuitcomponents or blocks (e.g., filters, amplifiers, passive components, andpossibly additional ICs) into one package. The ICs and/or modules arethen typically combined with other components, often on a printedcircuit board, to form part of an end product such as a cellulartelephone, laptop computer, or electronic tablet, or to form ahigher-level module which may be used in a wide variety of products,such as vehicles, test equipment, medical devices, etc. Accordingly,embodiments of the invention include RF filter circuits based on aplurality of AWRs in accordance with the teachings of this disclosureincorporated into a module configured to be combinable with othercomponents, wherein the module may include one or more additionalcircuit components or blocks. Through various configurations of modulesand assemblies, such ICs typically enable a mode of communication, oftenwireless communication.

CONCLUSION

A number of embodiments of the invention have been described. It is tobe understood that various modifications may be made without departingfrom the spirit and scope of the invention. For example, some of thesteps described above may be order independent, and thus can beperformed in an order different from that described. Further, some ofthe steps described above may be optional. Various activities describedwith respect to the methods identified above can be executed inrepetitive, serial, and/or parallel fashion.

It is to be understood that the foregoing description is intended toillustrate and not to limit the scope of the invention, which is definedby the scope of the following claims, and that other embodiments arewithin the scope of the claims. In particular, the scope of theinvention includes any and all feasible combinations of one or more ofthe processes, machines, manufactures, or compositions of matter setforth in the claims below. (Note that the parenthetical labels for claimelements are for ease of referring to such elements, and do not inthemselves indicate a particular required ordering or enumeration ofelements; further, such labels may be reused in dependent claims asreferences to additional elements without being regarded as starting aconflicting labeling sequence).

What is claimed is:
 1. A radio frequency filter circuit based on aplurality of acoustic wave resonators (AWR) and having a specified notchband and a specified passband, the radio frequency filter circuit andincluding: (a) at least one series-arm each including: (1) a series-armAWR having an electrostatic capacitance CO and selected to have aresonance frequency and an anti-resonance frequency associated with theseries- arm AWR, wherein the anti-resonance frequency is within thespecified notch band, and the resonance frequency and the anti-resonancefrequency are both spaced apart in frequency from the specifiedpassband; and (2) a series-arm matching inductor coupled in series withthe series-arm AWR to form a first inductor-capacitor circuit and havingan inductance value that resonates with the electrostatic capacitance C0of the series-arm AWR within the specified passband; and (b) at leastone parallel-arm coupled to the at least one series-arm and including:(1) a parallel-arm AWR having an electrostatic capacitance C0 andselected to have a resonance frequency and an anti-resonance frequencyassociated with the parallel-arm AWR, wherein the resonance frequency iswithin the specified notch band, and the resonance frequency and theanti-resonance frequency are both spaced apart in frequency from thespecified passband; and (2) a parallel-arm matching inductor coupled inparallel with the parallel-arm AWR to form a second inductor-capacitorcircuit and having an inductance value that resonates with theelectrostatic capacitance CO of the parallel-arm AWR within thespecified passband; wherein the anti-resonance frequency of the at leastone series-arm and the anti-resonance frequency of the coupled at leastone parallel-arm are selected to form a notch filter; wherein the firstinductor-capacitor circuit and the selection of the resonance andanti-resonance frequencies of the at least one series-arm AWR spacedapart from the specified passband makes the at least one series-arm AWRbehave like a short-circuit within the specified passband; wherein thesecond inductor-capacitor circuit and the selection of the resonance andanti-resonance frequencies of the at least one parallel-arm AWR spacedapart from the specified passband makes the at least one parallel-armAWR behave like an open circuit within the specified passband.
 2. Theinvention of claim 1, further including a series-arm notch tuningcircuit coupled in parallel with the series-arm AWR.
 3. The invention ofclaim 2, wherein the series-arm notch tuning circuit includes at leastone of an adjustable series-arm tuning inductor or an adjustableseries-arm tuning capacitor configured to change at least one of a notchcenter frequency, a notch width, and/or a notch depth of the radiofrequency filter circuit.
 4. The invention of claim 1, further includinga parallel-arm notch tuning circuit coupled in series with theparallel-arm AWR.
 5. The invention of claim 4, wherein the parallel-armnotch tuning circuit includes at least one of an adjustable parallel-armtuning inductor and/or an adjustable parallel-arm tuning capacitorconfigured to change at least one of a notch center frequency, a notchwidth, and/or a notch depth of the specified notch band of the radiofrequency filter circuit.
 6. The invention of claim 1, further includinga series-arm AWR matching adjustment circuit coupled in series with theseries-arm AWR and the series-arm matching inductor.
 7. The invention ofclaim 6, wherein the series-arm AWR matching adjustment circuit includesa series-arm match-adjustment capacitor which, in combination with theseries-arm matching inductor, provides an adjustable effectiveinductance configurable to resonate with the electrostatic capacitanceC0 of the series-arm AWR within the specified passband.
 8. The inventionof claim 1, further including a parallel-arm AWR matching adjustmentcircuit coupled in parallel with the parallel-arm AWR and theparallel-arm matching inductor.
 9. The invention of claim 8, wherein theparallel-arm AWR matching adjustment circuit includes a parallel-armmatch-adjustment capacitor which, in combination with the parallel-armmatching inductor, provides an adjustable effective inductanceconfigurable to resonate with the electrostatic capacitance C0 of theparallel-arm AWR within the specified passband.
 10. The invention ofclaim 1, further including a series-arm notch tuning circuit coupled inparallel with the series-arm AWR and a parallel-arm notch tuning circuitcoupled in series with the parallel-arm AWR.
 11. The invention of claim10, wherein the series-arm notch tuning circuit and the parallel-armnotch tuning circuit each include an adjustable circuit including atleast one of an adjustable tuning inductor and/or an adjustable tuningcapacitor and configured to change at least one of a notch centerfrequency, a notch width, and/or a notch depth of the specified notchband of the radio frequency filter circuit.
 12. The invention of claim1, further including a series-arm AWR matching adjustment circuitcoupled in series with the series-arm AWR and the series-arm matchinginductor, and a parallel-arm AWR matching adjustment circuit coupled inparallel with the parallel-arm AWR and the parallel-arm matchinginductor.
 13. The invention of claim 12, wherein the series-arm AWRmatching adjustment circuit and the parallel-arm AWR matching adjustmentcircuit each include a respective match-adjustment capacitor configuredto adjust the resonance of the coupled matching inductor with theelectrostatic capacitance C0 of the coupled AWR within the specifiedpassband.